Heretofore, a fuel tank for an internal combustion engine is closed with a filler cap in a case where the engine is mounted on a car (a passenger vehicle, a truck, an agricultural machine, a power generator, a mower, a motorbike, a scooter, a construction machine or the like). As fuel stored in the fuel tank is consumed, air needs to be introduced into a container from the outside to compensate for a volume of the consumed fuel of the tank. For this purpose, the filler cap is provided with an air passage. Moreover, in a case where the fuel tank disposed in the car tilts, there is a danger that a large amount of the fuel leaks from the air passage disposed at the filler cap and that the fuel which has leaked catches fire.
Furthermore, when the fuel tank tilts, a liquid surface of the fuel stored in the fuel tank rises above the air passage disposed at the filler cap. When the fuel enters the filler cap from the air passage, the fuel is adsorbed by sponge disposed beforehand in the filler cap. Alternatively, a chamber is disposed at the air passage which communicates with the outside in order to save a time elapsed until the fuel flows outwards. The filler cap structured in this manner does not contain a valve mechanism which stops inflow of the fuel, and has a danger that the fuel which has entered the cap leaks outwards in a short time to develop fire and air pollution.
Furthermore, in some case, a fuel inlet of the fuel tank is provided with a long tube, and a tip end of the tube (the fuel inlet) is closed with the filler cap to prevent the fuel from leaking from the filler cap. However, when the fuel tank falls, the liquid surface of the fuel tank rises above the filler cap at the tip end, and there is not any effect that the fuel is prevented from leaking out of the fuel inlet. In a case where a rollover valve is attached which inhibits the fuel from leaking outwards only when the fuel tank tilts, the outflow of the fuel can be stopped. However, a structure of the fuel tank has to be changed, and the changed structure is inconvenient during oil supply, and becomes expensive.
Another technology is proposed in order to prevent a large amount of the fuel stored in the fuel tank from leaking out of the air passage disposed at the filler cap. That is, the filler cap of the fuel tank is provided with a concave and convex portion forming a meandering passage to constitute a part of the air passage at a gap between an outer lid and a receiving portion for an inner lid. This meandering passage allows an only gas evaporated from the fuel stored in the fuel tank to flow from the filler cap, and the concave and convex portion inhibits the fuel from flowing outwards. In consequence, the leakage of the fuel from the fuel tank to the outside is reduced (e.g., see Japanese Patent Application Laid-Open No. 6-219461).
On the other hand, air pollution due to floating particulate substances and photochemical oxidant raises a serious problem. Even at present, an adverse influence of the floating particulate substances on human health is regarded as a problem, and the problem needs to be solved urgently. Moreover, VOC (generic organic compounds which change to a gas in the atmosphere) is one of the substances, and examples of VOC include toluene, xylene, ethyl acetate and fuel (gasoline). It is also regarded as a problem that the VOC gas evaporated from the fuel stored in the fuel tank is discharged from the air passage disposed at the filler cap to the atmosphere.
To solve the problem, it is also proposed that a disadvantage that the gas evaporated from the fuel stored in the fuel tank is discharged to the atmosphere should be prevented. In this case, the fuel tank is successively connected to the rollover valve, a canister and the engine via a piping line. Moreover, when the engine stops (the fuel tank is horizontally disposed), the gas evaporated in the fuel tank is adsorbed by an active carbon disposed at the canister. Moreover, when the engine starts, the gas adsorbed by the active carbon is desorbed, and the gas is sucked into the engine via a vaporizer and burnt. In consequence, the gas evaporated from the fuel stored in the fuel tank is prevented from being discharged from the filler cap to the atmosphere (e.g., see Japanese Patent Application Laid-Open No. 5-133287).
However, the filler cap of the former fuel tank has an effect of reducing the leakage of the fuel to the outside in a case where the fuel tank tilts. However, when the tilted state of the fuel tank continues for a predetermined time, an increasing amount of the fuel leaks from the air passage disposed at the filler cap. Therefore, there is still a danger that the fuel which has leaked catches fire.
Moreover, the latter fuel tank is connected to the rollover valve and the canister via the piping line, and the active carbon is disposed in this canister. Furthermore, the gas evaporated from the fuel stored in the fuel tank is adsorbed/desorbed with respect to the active carbon and burnt by the engine to prevent the fuel from being discharged from the filler cap to the atmosphere. However, the fuel tank requires the rollover valve for preventing the fuel from entering the canister from the fuel tank. Therefore, there has still been a problem that cost of the engine increases.
Moreover, there has been a demand for development of an inexpensive filler cap having a satisfactory appearance in which the fuel does not easily flow from the air passage of the filler cap at a time when the fuel tank tilts.
The present invention has been developed to solve such a problem of the conventional technology, and an object thereof is to provide a filler cap of a fuel tank capable of securely preventing a disadvantage that fuel stored in the fuel tank leaks from an air passage disposed at a cap main body.